recursive functions in typescript/javascript

Question

I am trying to call the following function recursively.

 public  getData(key,value){

   this.htmlString += '<span style="color:cornflowerblue">'+key+' </span>:';

    if(value instanceof Object){
      Object.keys(value).forEach(function (keydata) {
        let obj = value[keydata];
        this.getData(keydata,value[keydata]);

        console.log(key,obj,obj instanceof Object)
      });
    }else{
      this.htmlString += '<span>'+value+'</span>';
    }
    return this.htmlString;
  };

when i tried to call teh function it was showing an error " Cannot read property 'getData' of undefined. Is there any wrong in the code or any other way to do this.

Max Koretskyi · Accepted Answer · 2017-04-19 08:24:15Z

18

forEach accepts a callback, which is an anonymous function, and this inside anonymous function refers to window in non-strict mode or undefined in strict mode.

You need to bind context:

  Object.keys(value).forEach(function (keydata) {
    let obj = value[keydata];
    this.getData(keydata,value[keydata]);

    console.log(key,obj,obj instanceof Object)
  }.bind(this));

or use an arrow function:

  Object.keys(value).forEach((keydata) => {
    let obj = value[keydata];
    this.getData(keydata,value[keydata]);

    console.log(key,obj,obj instanceof Object)
  });

or simply pass pointer to this as a second argument to forEach:

  Object.keys(value).forEach(function (keydata) {
    let obj = value[keydata];
    this.getData(keydata,value[keydata]);

    console.log(key,obj,obj instanceof Object)
  }, this);

edited Apr 19, 2017 at 8:24

answered Apr 19, 2017 at 7:55

Max Koretskyi

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4 Comments

RobG Over a year ago

You can also pass a thisArg as a second parameter. this isn't "context", it's a parameter of an execution context.

Max Koretskyi Over a year ago

@RobG, thanks, I didn't know that. That's probably something new. I've edited the answer

RobG Over a year ago

It was introduced with forEach in ECMAScript ed 5. ;-)

Max Koretskyi Over a year ago

@RobG, interesting, I must have missed it. Thanks!

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